1. Field of the Invention
The ability to reorient DNA segments to provide for expression of heterologous genes in microorganisms provides numerous opportunities to synthesize peptides of physiological and commercial interest. In most instances, it will be desirable to maximize the production of the protein or peptide of interest while still maintaining cell viability. A number of different ways can be employed to improve the production of a desired poly(amino acid) product. For example, by employing plasmids having high copy numbers, the number of genes which are being expressed will also be multiplied. Another technique is to use the regulatory genes involved with expression of a structural gene which codes for a poly(amino acid) which is produced in high yield. Other techniques may also be available, such as increasing the lifetime of the messenger RNA, enhancing the transcription of the DNA by employing activators, enhancing ribosomal binding, or the like.
2. Description of the Prior Art
Hitzeman, Clarke and Carbon (1980) J. Biol. Chem 255: 12073-12080 describe a plasmid having a yeast 3-phosphoglycerokinase PGK gene and accompanying regulatory signals capable of expression in yeast. Gray et al. (1975) Nucleic Acid Research 2: 1459-1492 and Legerski et al. ibid 5: 1445-1464 describe the properties and use of the double stranded exonuclease BAL 31. Scheller et al. (1977) Science 196: 177-180 describe the use of linkers having restriction sites. Complementation with a leu gene in bacteria and yeast is described by Ratzkin and Carbon (1977) PNAS USA 74: 487-491 and Hinnen et al. (1978) ibid 75: 1929-1933, respectively.